All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background.
Disclosed in the embodiments herein are caster suspension systems designed to accommodate uneven or irregular surfaces. In one embodiment, there is provided a caster suspension system that employs a linkage between the two casters constraining one to rise when the other falls while keeping moment internal to the system such that there is no tipping of the load carried by the caster suspension system.
Casters are well known devices that assist in the mobility of a great variety of types of equipment. They are used in industry, in the home, in the medical field, and in general whenever it is desirable to move objects over a surface.
While casters function well on smooth surfaces they tend to operate less efficiently when used on uneven surfaces or surfaces which contain irregularities, or when small objects placed upon the surface are encountered by the casters. Accordingly casters have been devised which are better adapted to maneuver over uneven surfaces. However, such prior types of devices have functional characteristics which limit their suitability for certain applications.
Certain types of casters when used on uneven surfaces are inherently unstable and can cause objects supported by them to easily tip. The possibility of tipping is increased under certain circumstances, such as when changing direction or when such a type of caster is supporting and moving a load and then encounters an object on the surface which tends to restrict its forward travel.
Other certain special types of casters significantly and abruptly change their height when contacting objects on the surface. This, in turn, causes a bump which appears to abruptly change the height of the object that is supported by such a caster.
Still other prior types of casters are able to operate only one time, and must be reset after encountering an object. Still yet other prior types of casters tend to impact with objects located upon the surface, or when they encounter uneven surfaces, which in turn results in shock being transferred to the object supported.
Reaction forces and vibrations due to uneven positioning of an instrument with respect to the floor may be particularly problematic with precision instruments (such as photolithography machines used in semiconductor processing). For instance, a photolithography machine which is subject to vibratory motion may cause an image projected by the photolithography machine to move and, as a result, be aligned incorrectly on a projection surface such as a semiconductor wafer.
For several industry products, such as high production copiers/printers, their main structure has to be designed considering the effect of uneven floor to frame integrity. If the machine does not have a relatively rigid frame and is under an uneven floor scenario (e.g., fourth caster is not co-planar with three other casters), the frame may distort and create unpredictable alignments among the internal frame components, resulting in problems such as paper registration issues, copy quality and mechanical interference between components. While one may compensate for uneven floor effect by implementing a caster adjustment (de-racking) procedure at the site, the procedure may be inaccurate due to a failure to determine a realistic reference to which to square the machine frame. Another disadvantage is that if the machine is moved, the frame will deflect again and may need to be adjusted. The latter affects service trouble-shooting and installation lines.
FIGS. 1 and 2 illustrate prior art systems 10 employing a single four-bar linkage. In FIG. 1, casters 25, 25′ are positioned in opposing directions and are linked through link connections 20, 20′ to linkage bar 15. As moments 30, 30′ are in opposition directions, load 40 is balanced. However, when casters 25, 25′ are moved so as to be pointing in the same direction as shown in FIG. 2, moments 35, 35′ are in the same direction and load 40 is not balanced and will tip. Accordingly, there exists today a need for a caster that is articulated to accommodate uneven surfaces and which is inherently stable.